In general, a silver halide color photographic material is composed of a support base and silver halide emulsion layers coated thereon, of which each is sensitive or sensitized to a different region of the visible spectrum and contains a coupler capable of reacting with the oxidation products of a color developer to give a dye. For instance, a conventional color photographic material contains silver halide emulsion layers each of which is sensitive or sensitized to red light, to green light and to blue light and contains a cyan, magenta and yellow coupler, respectively. After exposure to light, the photographic material is submitted to color development to form cyan, magenta and yellow color images, respectively.
In particular, a reversal processing for the formation of a color image comprises a black and white development (with hydroquinone-phenidone) of an image-wise exposed multilayer color photographic element, the exposure or uniform fogging of the residual silver halide and the color processing which includes a color development, or second development (with p-phenylene diamine, for example), bleaching, fixing (or bleach-fixing) and a final stabilizing washing. Said color or second development is generally indicated in the photographic art as "reversal development".
To assure the necessary sharpness of the color image, the obtained dyes should not substantially diffuse in the layer where they are formed. To this purpose couplers provided with particular anti-diffusion or ballasting groups are used, which prevent the diffusion thereof. Said couplers are introduced into the photographic layer according to the oil dispersion method. Said method, described for instance in U.S. Pat. Nos. 2,322,027; 2,801,170; 2,801,171; 2,949,360 and 2,991,177, briefly consists of dissolving-the coupler in a high-boiling water-immiscible organic solvent (the oil), mechanically dispersing the solution in a hydrophilic colloid (e.g. gelatin) under the form of very small droplets and adding the obtained dispersion to the silver halide photographic emulsion.
In these multilayer photographic materials, the sensitometric properties (sensitivity, contrast and color maximum density) are well-balanced to obtain the best possible photographic image. The sensitometric properties of the photographic material are therefore desired not to change during storage both prior to and after light exposure untill it is developed.
It is known that formaldehyde and other aldehydes, even in traces in a gaseous state, are capable of reacting with the couplers used for the production of color images and thereby decreasing color density and causing fog formation in color photographic materials. This is especially true with 4-equivalent magenta couplers which have a reactive methylene group, and most particularly with 5-pyrazolone magenta couplers. Care is therefore taken by the manufacturers of color photographic materials to prevent such materials from being exposed (e.g. in the coating and drying plants of the photographic material) to traces of formaldehyde or other aldehydes, compounds which sometimes are used (e.g. as hardeners) in the manufacture of black and white photographic materials.
The photographic material however may come into contact with other formaldehyde traces during storage thereof prior to and after exposure. In manufacturing and commercial environments, objects capable of being sources of formaldehyde traces are often used; for instance building materials and furniture are treated with formaldehyde, there are adhesive substances containing formaldehyde as hardener, containers are made of formaldehyde resins, leathers are tanned with formaldehyde, and cloths are sterilized with formaldehyde. There are therefore many instances where a photographic material may come into contact with formaldehyde traces.
In the art it is known that the negative effect of formaldehyde traces can be decreased by increasing the relative quantity of oil with respect to the coupler to be dispersed, as described for instance in U.S. Pat. No. 4,490,460; the effect however is limited and the physical characteristics of the photographic layer turn out to be damaged by the presence of oil.
It is known as well that the use of 2-equivalent magenta couplers, which are less reactive towards formaldehyde, decreases the negative effect of formaldehyde; said couplers however are often chemically-unstable, have a low reactivity and tend to produce fog.
It has been proposed also to incorporate a compound reacting with formaldehyde into the coupler-containing layer in order to decrease the formaldehyde effect upon the sensitometric properties of the photographic material. Compounds which react with formaldehyde to be used in photographic materials containing 4-equivalent magenta couplers dispersed in oil are described for instance in GB Pat. No. 2,110,832, U.S. Pat. Nos. 3,652,278; 3,770,431; 3,811,891; 4,411,987 and 4,490,460. However, these compounds have some limits: some of them for instance have a limited capability of reacting with gaseous formalin, others are to be used in so large quantities that the physical characteristics of the photographic material are damaged, others interfere with the gelatin hardeners, and others have negative interactions with the photographic characteristics of the photographic material.
In the color photographic art, in particular in the art of the image formation in a color reversal process, there is therefore the need of providing a process which decreases the degradation of the sensitometric properties, such as color density decrease and fog increase in a silver halide color photographic material even when the material has been put into contact with formaldehyde traces for a long storage period prior to being developed.